378 REPORT OF THE CHEMIST OF THE 
higher sulphides decompose, forming lower sulphides, sulphides 
containing less sulphur in combination with calcium, or, stated 
another way, more calcium in combination with sulphur. 
From the point of view now generally held, though not ex- 
perimentally established, that the pentasulphide of calcium 
(CaS,;) is the most effective compound in the lime-sulphur 
wash for destroying scale-insects, it is obvious that the loss in 
efficiency by conversion of this sulphide into lower forms along 
with formation of thiosulphate and free sulphur as a result of 
treatment with lime, may be considerable. Thus, for 100 
pounds of sulphur in a concentrated wash there may be a loss 
of sulphide sulphur ranging from 12 to 36 pounds and averag- 
ing about 25 pounds; and, in addition to this, is supposed loss 
of efficiency by conversion of pentasulphide and tetrasulphide 
into forms of sulphide containing less sulphur. In fact, it can 
be seen that when a lime-sulphur wash is treated with lime be- 
fore application, it is highly probable that little or no calcium 
pentasulphide or tetrasulphide is applied to the trees, but only 
lower forms, together with thiosulphate and free sulphur. This 
whole question of change of efficiency in the lime-sulphur wash 
as a scale destroyer can be determined only by practical work 
on the part of entomologists. 
USE OF SEDIMENT IN MAKING LIME-SULPHUR WASH. 
It has been customary to throw away the portion remaining 
undissolved in the preparation of the lime-sulphur wash. The 
question has arisen as to whether this sediment cannot be used 
again along with more sulphur and lime in making more of the 
sulphide mixture. Our data bearing on the composition of the 
sediment enable us to give some information on this point. The 
sediment consists largely of calcium sulphite (CaSO,), free sul- 
phur, hydroxide and carbonate of lime and, in case of impure 
limestone, more or less hydroxide and carbonate of magnesium. 
When lime of good purity (containing over 90 per ct. of cal- 
cium oxide, and not more than 38 or 4 per ct. of magnesium 
oxide) is used, there will ordinarily be economy in using the 
sediment again, in order to utilize the free sulphur and eal- 
cium hydroxide it contains, In the case of lime containing 95 
